Solder masks are patterned films or layers which are designed to permanently overlie the printed circuitry on a printed circuit board. Patterned open areas of a solder mask selectively permit solder to adhere to metal of the printed board. The solder mask also protects the circuitry against short-circuiting.
Because solder masks are designed to provide a permanent layer, hardness and durability of the layer are considered important features of a solder mask composition. Generally, the solder mask is the outer layer of the printed circuit board; thus, appearance is also importance.
Photoimageable compositions may be applied to a printed circuit board by a variety of methods, such as screen printing, electrostatic spray coating, curtain coating or as a layer or laminate of a dry film. It is therefore desirable that a photoimageable composition coat a printed circuit board in a variety of application methods.
It is a general object of the present invention to provide an improved photoimageable composition which may be applied to a printed circuit board, photoimaged, developed with an alkaline aqueous developer and cured to form a hard, permanent solder mask. The permanent solder mask will withstand plating solutions (metal depositing baths) which operate in the range of pH 12 and above.